Since entering orbit around Jupiter last July, NASA's Juno probe has circled the gas giant every 53 days. This week, scientists are publishing the results of the orbiter's first data collection pass, with complex storm systems and an unexpectedly strong and lumpy magnetic field some of the Jovian features to catch them by surprise.
"We knew, going in, that Jupiter would throw us some curves," said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio. "But now that we are here we are finding that Jupiter can throw the heat, as well as knuckleballs and sliders. There is so much going on here that we didn't expect, that we have had to take a step back and begin to rethink of this as a whole new Jupiter."
One of the surprises came courtesy of the orbiter's imaging device JunoCam, with images revealing both of Jupiter's poles to be shrouded in Earth-sized cyclones. These systems are made up of densely clustered storms that appear to be rubbing together.
"We're puzzled as to how they could be formed, how stable the configuration is, and why Jupiter's north pole doesn't look like the south pole," said Bolton. "We're questioning whether this is a dynamic system, and are we seeing just one stage, and over the next year, we're going to watch it disappear, or is this a stable configuration and these storms are circulating around one another?".
Something else the scientists weren't expecting was the strength of the planet's magnetic field. Well, sort of. Before Juno launched, scientists already knew that Jupiter boasted the most intense magnetic field of any planet in the solar system. But measurements taken by Juno's magnetometer have revealed the field is even stronger than once thought, at 7.766 Gauss. Gauss is a standard unit of measurement for magnetic induction, and this figure makes Jupiter's magnetic field 10 times stronger than any found on Earth.
"Juno is giving us a view of the magnetic field close to Jupiter that we've never had before," said Jack Connerney, Juno deputy principal investigator. "Already we see that the magnetic field looks lumpy: it is stronger in some places and weaker in others. This uneven distribution suggests that the field might be generated by dynamo action closer to the surface, above the layer of metallic hydrogen. Every flyby we execute gets us closer to determining where and how Jupiter's dynamo works."
Another handy skill in Juno's repertoire is that it can investigate what exactly is going on beneath Jupiter's turbulent cloud tops. Its Microwave Radiometer, one of eight scientific instruments aboard Juno, helps with this by sampling thermal microwave radiation within its atmosphere. Data from this tool has found a variety of ammonia belts among Jupiter's iconic bands, with one near the equator actually penetrating hundreds of kilometers into the planet, farther than Juno can see.
Juno actually spends the majority of its time far away from Jupiter, out in space. This so-called elliptical orbit is a clever way of keeping the probe safe from the planet's destructive radiation. Every 53 days it swoops in for a closer look, grabbing as much data as it can while transiting between the poles in a daring two-hour flyby. It will continue this pattern until at least July next year, so we can expect a few more surprises before the mission comes to an end.
"On our next flyby on July 11, we will fly directly over one of the most iconic features in the entire solar system – one that every school kid knows – Jupiter's Great Red Spot," says Bolton. "If anybody is going to get to the bottom of what is going on below those mammoth swirling crimson cloud tops, it's Juno and her cloud-piercing science instruments."
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